Acreage Calculator
Turn field measurements into acres — rectangles, triangles, pivots and trapezoids, in feet, yards, chains or meters.
Your numbers
Area of this rectangle
20.0 acres
- Grazable acres after deductions
- 20.0 acres
- Square feet
- 871,200 ft²
- Hectares
- 8.1 ha
- Perimeter is about 3,960 ft — roughly 0.75 miles of fence to enclose it.
- Use the grazable figure, not the deeded figure, in any stocking rate or paddock calculation.
Show the math
- UnitsMeasurements already in feet
- Area1,320 ft × 660 ft = 871,200 ft²
- Convert to acres871,200 ft² ÷ 43,560 ft²/acre = 20.00 acres
- Non-grazable groundNone deducted
Assumptions this calculator used
Nothing here is hidden. Change any figure you have better local data for.
- 43560 ft²
Fixed legal definition — one chain by one furlong. Source: US customary units.
- 0.404686 ha
Used for the metric conversion shown alongside the result. Source: International yard and pound agreement, 1959.
How to calculate acreage
Acreage is an area calculation with one conversion on the end. Measure the field in a single unit, apply the formula for its shape to get square feet, then divide by 43,560.
Acres = area in ft² ÷ 43,560
Worked example
A field measuring 1,320 ft by 660 ft covers 871,200 square feet. Divided by 43,560 that is exactly 20 acres — the classic quarter-mile by eighth-mile block of the Public Land Survey grid. If 15% of it is timber and pond, you have 17 grazable acres, and that is the number to carry into a stocking rate run.
Common mistakes
- Mixing units. Measuring one side in yards and the other in feet produces an answer three times too large or small.
- Using a circle's diameter as its radius. That overstates a pivot field by four times.
- Using a trapezoid's slanted side as the height. The height is the perpendicular distance between the parallel sides.
- Trusting the deed acreage. Old descriptions include roads and creek beds, and the boundary may have moved since the survey.
Common field shape formulas and land measures
The area formulas used above, plus the land measures that show up in American deeds, leases and section descriptions.
| Shape or measure | Formula / equivalent | Example |
|---|---|---|
| Rectangle or square | length × width | 1,320 × 660 ft = 20 acres |
| Triangle | (base × height) ÷ 2 | 1,000 × 800 ft ÷ 2 = 9.18 acres |
| Circle (center pivot) | π × radius² | 1,320 ft radius = 125.7 acres |
| Trapezoid | ((side A + side B) ÷ 2) × height | (900 + 600) ÷ 2 × 700 = 12.05 acres |
| Right triangle from two legs | (leg A × leg B) ÷ 2 | 660 × 660 ft ÷ 2 = 5 acres |
| 1 acre | 43,560 ft² | 208.71 ft square |
| 1 acre | 0.4047 hectares | 4,047 m² |
| 1 hectare | 2.471 acres | 10,000 m² |
| 1 chain | 66 ft (4 rods) | 10 sq chains = 1 acre |
| 1 rod | 16.5 ft | 160 sq rods = 1 acre |
| 1 furlong | 660 ft (10 chains) | 8 furlongs = 1 mile |
| 1 section | 1 sq mile = 640 acres | 5,280 ft square |
| Quarter section | 160 acres | 2,640 ft square |
| Quarter-quarter ('a forty') | 40 acres | 1,320 ft square |
Calculators to run next
- Stocking Rate CalculatorStart here when the question is how many cows the whole place will run for a season.
- Animal Unit Equivalent CalculatorUse when the herd is mixed, so one number stands in for every class on the place.
- Grazing Days CalculatorUse when the herd is already in the paddock and you need a move date.
- Forage Yield CalculatorRun this first — every other grazing number depends on pounds of dry matter per acre.
- Paddock Size CalculatorUse when you are subdividing ground and need acres per break and paddock count.
- Pasture Rest Period CalculatorUse when regrowth is falling short and the rotation needs to slow down.
Guides that use this calculator
- Fencing a Rotational Grazing System Without Overbuilding ItLay the paddocks out around water first. Order the posts second. Most people do it the other way and pay for it.
Questions ranchers ask
How many square feet are in an acre?
43,560 square feet. The figure comes from an old English chain measure — one acre is a strip one chain (66 ft) wide and one furlong (660 ft) long. It is also about 208.7 ft square, which is a handy mental picture when pacing off a field.
How do I calculate the acreage of an irregular field?
Break it into shapes you can measure — rectangles, triangles and trapezoids — calculate each, and add them together. Most odd fields split cleanly into two or three pieces. For genuinely irregular boundaries along a creek or fence line, a GPS track walked or driven around the perimeter is far quicker and more accurate than a tape.
Can I measure acres with my phone?
Yes. A GPS area app, or the measure tool in Google Earth, is usually within 2% to 5% for a field of a few acres, which is plenty for grazing planning. For anything that will end up in a deed, a lease payment or a cost-share contract, use a licensed surveyor.
What is a chain and why do old deeds use them?
A surveyor's chain is 66 feet, or 4 rods. Ten square chains make an acre, so the unit made acreage arithmetic simple before calculators. Plenty of American deeds and section descriptions are still written in chains and rods, so it is worth knowing the conversion.
How many acres is a section of land?
A full section is one square mile, or 640 acres. A quarter section is 160 acres, a quarter-quarter (a 'forty') is 40 acres. This Public Land Survey System grid runs across most of the country west of the original colonies and still shapes how ground is described and traded.
Should I use total acres or grazable acres for stocking rate?
Grazable acres, always. Subtract timber, ponds, rock outcrops, building lots, roads and any ground cattle cannot reach or will not use. Using deeded acres is one of the most common causes of accidental overstocking.
How do I convert acres to hectares?
One acre is 0.4047 hectares, and one hectare is 2.471 acres. A quick field approximation is to divide acres by 2.5. This calculator reports both.
Is a circular pivot field really the diameter I think it is?
Usually not. A quarter-section pivot with a 1,320 ft radius covers about 126 acres out of the 160-acre quarter, because the corners are outside the circle. Corner arms add roughly 10 to 20 acres depending on the machine.
Know the acres, then match the cattle to them
Once you have the grazable acreage, the next question is how many head it will run. Take that figure into the stocking rate calculator, and when you are buying, Agrilot's auctions list registered Angus cattle with full performance records and an independent condition report on every lot.